一般性雙希格斯二重態模型中的電偶極矩

Abstract

在過去的大約50年間，不含重力的所有基本物理學都由粒子物理的「標準模型」所涵蓋。標準模型提供了一個統一性的數學架構，解釋了許多原子和次原子層級的現象，更提出了一連串的預測，其中有許多已經透過實驗以極高的精確度去驗證。雖然如此，還是存在一些標準模型尚無法解釋的疑問，其中一個是現存物質與反物質數量的不平衡，又稱「宇宙重子不守恆」。受此（和其他）疑問的啟發，有許多人嘗試提出標準模型之延伸理論模型。當中有一個系列的理論模型多加入了一組（性質不盡相同的）希格斯二重態，稱之為「雙希格斯二重態模型」。在這些雙希格斯二重態模型中，有一種沒有提出任何預先性的對稱性或耦合限制，被稱作「一般性雙希格斯二重態模型」。這些試圖解釋宇宙重子不守恆的理論模型都有一個特色，就是內含為數不小的CP違逆。在實驗方面，因欠缺新的對撞機實驗觀測結果，且低能量精準測量實驗的實驗數值極小，這對宇宙重子不守恆的CP違逆形成了大幅度的限制。在這些實驗中，各基本粒子的電偶極矩值成了CP違逆所造成之效應的決定性測試。此篇研究旨在分析一般性雙希格斯二重態模型中的各種基本粒子電偶極矩值。我們從電子電偶極矩出發，提出一個相消效應，以提供足夠的參數空間，讓理論在解釋宇宙重子不守恆的同時，不被電偶極矩量測結果所限制。隨後，我們將理論框架延伸套用至緲子和濤子，並呈現此二較重之輕子的電偶極矩理論預測與實驗觀測。我們也透過中子電偶極矩來探究較輕之夸克電偶極矩相關效應，並同時納入膠子相關效應的影響。最後，我們呈現一個同時包含電子電偶極矩和中子電偶極矩的分析，並強調實驗的驗證，甚至是發現，在未來十年至二十年間極有可能達成。

The Standard Model (SM) of particle physics has been the dominant theory of all fundamental physics sans gravity for a good 50-or-so years. The SM provides a unifying mathematical framework, explanations for various atomic and subatomic phenomena, and a plethora of predictions, many of which have since been verified by experiments to high precision. Nevertheless, there are still questions the SM still does not have an answer for, one of them being the imbalance of naturally existing matter and antimatter, also known as the Baryon Asymmetry of the Universe (BAU). Motivated by this question (among others), there have been various theoretical attempts at extending beyond the Standard Model (BSM). One family of these extensions are the Two-Higgs Doublet Models (2HDMs), which propose an extra Higgs doublet with varying properties. Among these 2HDMs, one type does not have any assumed symmetry or coupling constraints, and is known as the General Two Higgs Doublet Model (G2HDM). A key feature of such theories attempting to address BAU is large charge-parity violation (CPV). On the experimental front, both the lack of new collider observations as well as the smallness of low-energy precision measurements put heavy constraints on BSM CPV. In particular, the electric dipole moments (EDMs) of various fundamental particles provide a litmus test for CPV effects. This study is an examination and analysis of various EDMs under the G2HDM framework. We start with the electron EDM (eEDM), introducing a cancellation mechanism that allows for an adequate parameter space to address the BAU issue while evading the current EDM bounds. We then extend the framework to the muon and the tau, and present both general and cancellation-imposed results for the EDM of heavier leptons. We also probe the effects of the light quark EDMs through the neutron EDM (nEDM), taking into account gluon-related contributions. At last, we present a combined scenario analysis of the eEDM and the nEDM, signifying that experimental verification, or even discovery, is achievable within the next decade or two.